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Also, document this functionality more prominently, including with a reference from sd_event_exit(). This is mostly to make things complete, as previously we supported NULL callbacks only in _add_time() and _add_signal(). However, I think this makes snese for IO event sources too (think: when some fd such as a pipe end sees SIGHUP or so, exit), as well as defer or post event sources (i.e. exit once we got nothing else to do). This also adds support for inotify event sources, simply to complete things (I can't see the immediate use, but maybe someone else comes up with it). The only event source type that doesn't allow callback=NULL now are exit callbacks, but for them they make little sense, as the event loop is exiting then anyway.
320 lines
16 KiB
XML
320 lines
16 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_event_add_time</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_event_add_time</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_event_add_time</refname>
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<refname>sd_event_source_get_time</refname>
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<refname>sd_event_source_set_time</refname>
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<refname>sd_event_source_get_time_accuracy</refname>
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<refname>sd_event_source_set_time_accuracy</refname>
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<refname>sd_event_source_get_time_clock</refname>
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<refname>sd_event_time_handler_t</refname>
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<refpurpose>Add a timer event source to an event loop</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
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<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
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<funcprototype>
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<funcdef>typedef int (*<function>sd_event_time_handler_t</function>)</funcdef>
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<paramdef>sd_event_source *<parameter>s</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_time</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>clockid_t <parameter>clock</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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<paramdef>uint64_t <parameter>accuracy</parameter></paramdef>
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<paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_time_relative</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>clockid_t <parameter>clock</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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<paramdef>uint64_t <parameter>accuracy</parameter></paramdef>
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<paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_time</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t *<parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_set_time</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_set_time_relative</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_time_accuracy</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t *<parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint64_t <parameter>usec</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_time_clock</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>clockid_t *<parameter>clock</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_event_add_time()</function> adds a new timer event source to an event loop. The event loop
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object is specified in the <parameter>event</parameter> parameter, the event source object is returned in the
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<parameter>source</parameter> parameter. The <parameter>clock</parameter> parameter takes a clock identifier, one
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of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>,
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<constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See
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<citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details
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regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in
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microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past
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is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be
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dispatched. If the parameter is specified as <constant>UINT64_MAX</constant> the timer event will never elapse,
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which may be used as an alternative to explicitly disabling a timer event source with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
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<parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the
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timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum
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accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed
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substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively,
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improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when
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the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be
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chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called
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slightly later, subject to the specified accuracy value, the kernel timer slack (see
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<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional
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scheduling latencies. To query the actual time the handler was called use
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<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>By default, the timer will elapse once
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(<constant>SD_EVENT_ONESHOT</constant>), but this may be changed
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with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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If the handler function returns a negative error code, it will be
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disabled after the invocation, even if the
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<constant>SD_EVENT_ON</constant> mode was requested before. Note
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that a timer event set to <constant>SD_EVENT_ON</constant> will
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fire continuously unless its configured time is updated using
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<function>sd_event_source_set_time()</function>.
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</para>
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<para><function>sd_event_add_time_relative()</function> is like <function>sd_event_add_time()</function>,
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but takes a relative time specification. It's relative to the current time of the event loop iteration,
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as returned by
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<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>To destroy an event source object use
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<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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but note that the event source is only removed from the event loop
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when all references to the event source are dropped. To make sure
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an event source does not fire anymore, even if it is still referenced,
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disable the event source using
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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with <constant>SD_EVENT_OFF</constant>.</para>
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<para>If the second parameter of
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<function>sd_event_add_time()</function> is
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<constant>NULL</constant> no reference to the event source object
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is returned. In this case the event source is considered
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"floating", and will be destroyed implicitly when the event loop
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itself is destroyed.</para>
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<para>If the <parameter>handler</parameter> parameter to <function>sd_event_add_time()</function> is
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<constant>NULL</constant>, and the event source fires, this will be considered a request to exit the
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event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as
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the exit code parameter to
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and
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<constant>CLOCK_REALTIME_ALARM</constant> to define event sources
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that may wake up the system from suspend.</para>
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<para>In order to set up relative timers (that is, relative to the
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current time), retrieve the current time via
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<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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add the desired timespan to it, and use the result as
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the <parameter>usec</parameter> parameter to
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<function>sd_event_add_time()</function>.</para>
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<para>In order to set up repetitive timers (that is, timers that
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are triggered in regular intervals), set up the timer normally,
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for the first invocation. Each time the event handler is invoked,
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update the timer's trigger time with
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<citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
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iteration, and reenable the timer using
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<function>sd_event_source_set_enabled()</function>. To calculate
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the next point in time to pass to
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<function>sd_event_source_set_time()</function>, either use as
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base the <parameter>usec</parameter> parameter passed to the timer
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callback, or the timestamp returned by
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<function>sd_event_now()</function>. In the former case timer
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events will be regular, while in the latter case the scheduling
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latency will keep accumulating on the timer.</para>
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<para><function>sd_event_source_get_time()</function> retrieves the configured time value of an event
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source created previously with <function>sd_event_add_time()</function> or
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<function>sd_event_add_time_relative()</function>. It takes the event source object and a pointer to a
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variable to store the time in, relative to the selected clock's epoch, in µs. The returned value is
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relative to the epoch, even if the event source was created with a relative time via
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<function>sd_event_add_time_relative()</function>.</para>
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<para><function>sd_event_source_set_time()</function> changes the time of an event source created
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previously with <function>sd_event_add_time()</function> or
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<function>sd_event_add_time_relative()</function>. It takes the event source object and a time relative
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to the selected clock's epoch, in µs.</para>
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<para><function>sd_event_source_set_time_relative()</function> is similar to
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<function>sd_event_source_set_time()</function>, but takes a time relative to the current time of the
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event loop iteration, as returned by <function>sd_event_now()</function>.</para>
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<para><function>sd_event_source_get_time_accuracy()</function>
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retrieves the configured accuracy value of an event source
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created previously with <function>sd_event_add_time()</function>. It
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takes the event source object and a pointer to a variable to store
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the accuracy in. The accuracy is specified in µs.</para>
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<para><function>sd_event_source_set_time_accuracy()</function>
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changes the configured accuracy of a timer event source created
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previously with <function>sd_event_add_time()</function>. It takes
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the event source object and accuracy, in µs.</para>
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<para><function>sd_event_source_get_time_clock()</function>
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retrieves the configured clock of an event source created
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previously with <function>sd_event_add_time()</function>. It takes
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the event source object and a pointer to a variable to store the
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clock identifier in.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, these functions return 0 or a positive
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integer. On failure, they return a negative errno-style error
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code. </para>
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<refsect2>
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<title>Errors</title>
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<para>Returned values may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Not enough memory to allocate an object.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>An invalid argument has been passed.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ESTALE</constant></term>
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<listitem><para>The event loop is already terminated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The event loop has been created in a different process.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EOPNOTSUPP</constant></term>
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<listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EDOM</constant></term>
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<listitem><para>The passed event source is not a timer event source.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EOVERFLOW</constant></term>
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<listitem><para>The passed relative time is outside of the allowed range for time values (i.e. the
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specified value added to the current time is outside the 64 bit unsigned integer range).</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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